Measuring and testing – Volume or rate of flow – By measuring transit time of tracer or tag
Patent
1982-09-09
1984-11-20
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
By measuring transit time of tracer or tag
73204, G01F 168
Patent
active
044832001
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hot-wire pulse flowmeter for use in measurement of the rate of flow of an expiration or inspiration, for example, for pulsatively heating the fluid being measured and detecting the heated fluid downstream of a position in which the fluid has been heated to thereby measure the speed of flow of the fluid.
BACKGROUND ART
It has been customary practice to measure the rate of flow of a fluid by heating the fluid with thermal pulses at an upstream position in a pipe through which the fluid flows, detecting the heated fluid at a position spaced a certain distance downstream from the position in which the fluid has been heated, and measuring an interval of time which has elapsed after the fluid has been heated and before the heated fluid is detected, for thereby measuring the speed of flow of the fluid. The average speed of flow v can be expressed as follows: cross-sectional area of the pipe through which the fluid flows.
Assuming that a heater unit located upstream in the pipe for heating the fluid is spaced from a thermosensitive unit disposed downstream of the heater unit in the pipe by a distance d (cm), and an interval of time T elapses after the fluid has been heated by the heater unit and before the heated fluid is detected by the thermosensitive unit, the following equation can be derived:
As can be seen from the equation (2), as the rate of flow L of the fluid increases, the time interval T decreases in inverse proportion. Conventional hot-wire flowmeters have heated the fluid periodically. It has been difficult to set the period at which the fluid is to be heated by the heater unit in a system in which the rate of flow of the fluid is subjected to large changes. More specifically, if the heating period were too large, then the measurement time would be prolonged and rapid changes in the rate of flow of the fluid could not be followed, resulting in a failure in proper measurements in which such rapid changes are reflected. If the heating period were too short, then the fluid as detected downstream in the pipe per unit time would be adversely affected by heating in a next period, with the result that detection of the heated fluid would be inaccurate.
Fluids to be measured are of a variety of compositions, available in a wide range of rates of flow, and are measured for their rates of flow under various conditions such as ambient temperature, pressure, and the like. Under such various conditions, the fluids are heated by the heater unit under varied conditions, and cannot be heated to a constant temperature. For example, as the speed of flow of the fluid increases, an increased amount of thermal energy is lost from the heater which is then reduced in resistance, and hence the fluid is heated less intensively. If the heated portion of the fluid had different temperatures at the thermosensitive unit, it would be unable to detect the heated portion of the fluid reliably.
It is an object of the present invention to provide a thermal pulse flowmeter having a wide range of measurements.
Another object of the present invention is to provide a thermal pulse flowmeter capable of measuring a fluid flowing at rapidly and largely changing rates, such as an expiration or inspiration.
DISCLOSURE OF THE INVENTION
According to the present invention, a heater is disposed in a pipe through which a fluid to be measured, and is supplied with thermal pulses from a heater circuit to heat the fluid pulsatively. A detector is mounted in the pipe downstream of the heater and is responsive to temperature for detecting passage of a heated portion of the fluid. Upon such detection, a drive timing signal is generated which drives the heater circuit again to heat the heater. The period of repetition at which the heater is heated is measured, and the rate or speed of flow of the fluid is displayed dependent on the measured period.
Thus, the heater is heated again in response to detection of passage of the heated fluid across the detector. The period at which the heater is heated b
REFERENCES:
patent: 4228683 (1980-10-01), Juffa et al.
patent: 4237730 (1980-12-01), Feng
Nemoto Tetsu
Togawa Tatsuo
Tsubakimoto Hirohisa
Anima Corporation
Goldstein Herbert
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